The present invention relates to a flexible shaft exhibiting reduced noise and vibration characteristics and is especially useful for, but not limited to a flexible shaft which couples a motor to a gear assembly for positioning an adjustable seat in a motor vehicle.
In automotive seat positioning systems currently in use, a drive motor is equipped with a female drive member typically having a square recess for receiving one square end of a flexible shaft. The opposite end of the flexible shaft is also square and engages a similar recess in a gearbox assembly which converts rotary motion to linear motion (for example, forward, rearward, upward, and downward) to move the seat accordingly.
In an effort to improve perceived value, the automotive industry strives for reduction of harshness due to noise and vibration, including buzz, squeak and rattle noise when the seat is moved.
Noise and vibration in the aforementioned seat adjustment mechanism is contributed to by relative movement and accompanying friction between the ends of the flexible shaft and the recesses with which those ends mate. Such relative movement is reduced by forming the shaft ends in a helical square configuration so that they more tightly engage the mating recesses, as taught by U.S. Pat. No. 6,464,588.
However, in order for the helical square shaft ends to significantly reduce vibration and noise the mating recesses must be dimensioned to rather close tolerances which are not always realized in production seat assemblies.
The use of nylon coatings on the flexible shafts ends to prevent metal to metal contact and thereby reduce friction and resulting vibration and noise is known in the art. Such coatings, however, have not proven to provide satisfactory performance in applications which are not of a light duty nature.
For a number of years flexible shaft end coatings have been applied utilizing electrostatic grade nylon 11 powder. A “volumized bed” or thermal coating process applies a thin (approximately 0.003 inches) layer of the nylon powder to the flexible shaft ends. The shaft is first heated to a specific temperature and then passed through a cloud of the powder, to partially melt the powder and fuse it to the flexible shaft ends. The resulting coating prevents direct metal to metal contact and reduces gaps between the shaft ends and mating recesses, reducing vibration and noise. However, over time the thickness of the coating is reduced due to mechanical working and wear, and noise levels increase.
Accordingly, an object of the present invention is to provide a flexible shaft exhibiting reduced vibration and noise over a long period of time and suitable for coupling to mating recesses having less tight tolerances; that is, a relatively wide variation from the nominal dimensions thereof.